1. Field of the Invention
This invention relates to a vibrating gyroscope for the accurate measurement of angular speed within a wide measurement range. This gyroscope has the advantage over techniques usually used of being simpler to use and therefore of being inexpensive while remaining accurate and requiring little space.
2. Description of the Prior Art
Vibrating gyroscopes are based on the action of the Coriolis forces caused by a rotation imposed on masses in motion.
Several embodiments have been proposed in the past for the production of a vibrating element sensitive to angular speed.
The method most frequently used consists in vibrating a cylindrical or hemispherical test piece perpendicularly to its axis, and in observing the vibration nodes when it is subjected to rotation about said axis.
The main difficulties stem from the means used to create and measure the vibration.
The solutions proposed to date for the creation of the vibration have mainly been of an electromagnetic, electrostatic or piezoelectric nature.
The main drawback of electrostatic solutions is that they require high electric voltages and, in order to be efficient, very small air gaps. To avoid arc ignition, the assembly must be in a vacuum which, in addition to the machining accuracy needed, is a very costly requirement.
The piezoelectric solutions use either a cylinder, entirely in piezoelectric material, or small piezoelectric elements mounted usually by bonding, onto a metal cylinder.
The use of small piezoelectric elements mounted onto a metal cylinder enables costs to be reduced somewhat, but hardly any improvement is made to performance due to the crossfeed caused by the masses of said ceramics located on particular points of the cylinder.
Another major difficulty with all these solutions resides in the fact that the detection signals are of very low electrical level and that it is very difficult to protect them from low-level excitation signals within the same frequency band. For this reason, the means for detecting and exciting the vibrations are usually of a different nature and, insofar as possible, far apart from one another.
U.S. Pat. No. 4,793,195 describes e.g. a vibrating cylinder gyroscope equipped with electrostatic detection and is magnetically excited at a frequency half that of its vibration frequency in order to reduce these effects.
French patent application No. 95/11211 describes a gyroscope with magnetic excitation and optical detection also well protected from the excitation signals.
This invention introduces a simplification to this latter type of gyroscope by suppressing the optical detection means and by using the electromagnetic excitation device itself to perform detection. Separation of the excitation and detection signals is achieved, on the one hand, by using an excitation at half frequency and, on the other hand, by distributing the polarisations and directions of winding so as to cancel interaction between excitation and detection. Another embodiment using multiplexing enables this separation to be further enhanced. The accuracy of the gyroscope obtained depends solely on the precision of highly conventional and therefore inexpensive mechanical machining as well as on electronic parameters that are easily mastered. This solution thus has the advantage of being even more economical.
The invention thus relates to a vibrating gyroscope of the type comprising:
a thin vibrating element generated by revolution,
an excitation means enabling the generation of vibrations at at least one point of the vibrating element so as to cause to appear, on said vibrating element, a succession of vibration nodes and bulges susceptible of moving under the effects of an angular speed of rotation, and
a means for detecting said vibrations, disposed so as to be able to detect said nodes and/or said bulges, characterized in that said excitation and detection means are both electromagnetic and made from the same electromagnetic assembly common to both the excitation and detection functions.
Embodiments of the invention will now be described, by way of non-limiting examples, in reference to the appended drawings in which: